1. Technical Field
Some example embodiments generally relate to an image forming apparatus and/or an image forming method, for example, for fixing a toner image on a recording medium.
2. Description of Background Art
A background image forming apparatus, for example, a copying machine, a facsimile machine, a printer, or a multifunction printer having copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data by an electrophotographic method. For example, a charger charges a surface of an image carrier (e.g., a photoconductor). An optical device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to image data. The electrostatic latent image is developed with a developer (e.g., toner) to form a toner image on the photoconductor. A transfer device transfers the toner image formed on the photoconductor onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet. The sheet bearing the fixed toner image is output onto an outside of the image forming apparatus.
An example fixing device includes a fixing roller pair (e.g., a heating roller and/or a pressing roller). A heat source (e.g., a halogen lamp) is disposed inside the heating roller. When a sheet bearing a toner image passes a nip formed between the heating roller and the pressing roller, the fixing roller pair melts and fixes the toner image on the sheet.
Another example fixing device includes a fixing belt looped over a plurality of support rollers. A pressing roller opposes one of the support rollers via the fixing belt. A heat source (e.g., a halogen lamp) is disposed inside the support roller. When a sheet bearing a toner image passes a nip formed between the fixing belt and the pressing roller, the fixing belt and the pressing roller melt and fix the toner image on the sheet.
The fixed toner image may have increased surface asperities scattering incident and output lights, resulting in a toner image having a decreased saturation and a color reproduction.
An image forming apparatus may form a high quality image on a sheet having decreased surface asperities and an increased gloss (e.g., art paper, coated paper, light weight coated paper, and/or the like). When a toner image having increased surface asperities and a decreased gloss is formed on a sheet having decreased surface asperities and an increased gloss, the toner image and the sheet have glosses different from each other, respectively, resulting in formation of a faulty toner image having a decreased uniform gloss.
For example, a halftone image on a sheet includes a toner area bearing toner and a non-toner area not bearing toner and thereby exposing a sheet. A halftone image having a small image area rate has an increased gloss equivalent to a gloss of a sheet because the halftone image bears a small amount of toner. A halftone image having a medium image area rate has a decreased gloss because the halftone image bears a great amount of toner. A halftone image having a large image area rate has a gloss varying depending on a melting condition of toner. Thus, the sheet bearing the halftone image has various glosses, resulting in formation of a faulty toner image.
To address this problem, an example background fixing device applies heat and pressure to a sheet bearing a fixed toner image to further fix the toner image in a state that a film contacts the toner image on the sheet. After the toner image is cooled down, the film is separated from the sheet, so as to increase a gloss of the toner image. However, the example background fixing device may include two fixing devices, resulting in a large size image forming apparatus.
Another example background fixing device uses a fixing belt to apply heat and pressure to a sheet bearing a toner image so as to fix the toner image on the sheet. The sheet bearing the fixed toner image is cooled down while the sheet is conveyed on the fixing belt in a state that the fixed toner image contacts the fixing belt. The cooled sheet is separated from the fixing belt. A plane surface of the fixing belt decreases surface asperities of the toner image and increases a gloss of the toner image. However, the fixing belt may have a large size in a sheet conveyance direction to cool down the sheet, resulting in a large size fixing device or image forming apparatus. The fixing belt may be alternately heated to fix a toner image on a sheet and cooled to cool down the sheet, preventing energy saving. Further, the fixing belt may not rotate at a high speed to cool down the sheet, resulting in a decreased productivity at a decreased print speed. A sheet bearing a toner image contacts and scrapes the plane surface of the fixing belt even when the plane surface of the fixing belt does not need to increase a gloss of the toner image, resulting in wear of the fixing belt. Thus, the fixing belt may not increase a gloss of a toner image on a sheet for a long time period.